Normally, my X server uses about 265MB of virtual memory. Loading a
game like Infiltration, or heavy 3D application makes it grow to
over 300MB at times. After exiting the application, X virtual process
size stayed at its maximum size.

That is standard behavior for most UNIX processes. The more addresses
a program requests, the more it is given, and they are only returned to
the OS if your application explicitly unmaps them. Not all OS can even
do that.

Since upgrading the driver, I noticed things had improved all around, so
today I took a good look at X memory use. Things have changed...

Now my X server uses an average of 76MB. Playing Infiltration moves
virtual size to 98MB. Exiting the game causes virtual size to shrink
back to 76MB.

It even shrinks after using things like The Gimp, and other image
programs.

I am wondering what nVidia did in this driver that makes such a big difference.